Indications for platelet transfusion: Bone marrow failure (due to disease, cytotoxic therapy and irradiation) In the absence of other risk factors, the patient requires platelet transfusion at a threshold value of 10×109/l, which is as safe as higher thresholds. Risk factors include sepsis, concomitant antibiotics, or other irregular bleeding (grade A, level Ib). In patients without any risk factors, the threshold may be 5×109/l if there is concern about the production of platelet antibodies by alloimmunization (grade B, level IIa). Setting a definitive threshold for patients with chronic persistent thrombocytopenia may not be appropriate and it is better to set an individual baseline based on the degree of bleeding (Class C, Level IV). Prophylactic transfusion for surgery Bone marrow aspiration and biopsy may be performed without platelet support in patients with severe thrombocytopenia if adequate surface compression is given. (C et al., Level V). For lumbar puncture, epidural anesthesia, gastroscopy and biopsy, indwelling tube insertion, bronchial biopsy, liver biopsy, cesarean section, or similar procedures, platelet counts should be at least 50×109/l (Grade B, Level III). For patients undergoing critical site surgery, such as brain or eye, platelet counts should be raised to 100×109/l (Grade C, Level V). Massive transfusion Recommended (Grade C, Level IV) For patients with acute bleeding, the consensus is that the platelet count should be no less than 50×109/l For patients with compound trauma or central nervous system injury it is recommended that the count level should be raised to 100×109/l Disseminated intravascular coagulation (DIC) Recommended (Grade C, Level IV) Platelet counts and coagulation factor assays are frequently evaluated. There is no consistent standard for an ideal platelet count, but maintaining a platelet count >50×109/L in high-volume blood loss is a reasonable measure. In chronic DIC or in the absence of bleeding, platelet transfusion should not be performed solely to correct a low platelet count. Cardiopulmonary bypass surgery Platelets should be readily available in hospitals performing cardiovascular surgery. The same recommendation should be used to manage conditions such as ruptured abdominal aortic aneurysms (National Confidential Intraoperative Mortality Survey, 2001) (Class C, Level IV). Platelets should be reserved for patients with excessive postoperative blood loss that excludes surgical causes (Class A, Level Ib). Preoperative monitoring of patients undergoing cardiovascular surgery should include a thorough examination for therapeutic measures that interfere with platelet function. If such conditions are present, consideration needs to be given to whether to postpone the procedure, use appropriate intraoperative pharmacotherapy (peptidase) or whether platelet transfusion is required. clinical judgment of platelet transfusion after CPB is based on evidence of microvascular bleeding and excessive postoperative blood loss (Slichter, 1980) (both Class C, Level IV). Immune thrombocytopenia Recommended (Class C, Level IV) Platelet transfusions should be prepared in advance for patients with life-threatening bleeding, such as gastrointestinal or genital tract bleeding, bleeding into the central nervous system or remaining sites associated with severe thrombocytopenia (BCSH, Guidelines for the Observation and Management of Idiopathic Thrombocytopenic Purpura in Children, Adults, and Pregnant Women). Due to the shortened platelet survival after transfusion, large amounts of concentrated platelets are required to ensure hemostasis. Additional therapeutic measures such as intravenous methylprednisolone and immunoglobulins should be applied simultaneously to minimize the risk of bleeding and to increase the platelet count. Contraindications to platelet transfusion Thrombotic thrombocytopenic purpura (TTP). Platelet transfusions are transiently associated with exacerbation of TTP and are therefore contraindicated unless there is life-threatening bleeding. Heparin-induced thrombocytopenia (HIT) Ineffective platelet transfusion The effect of platelet transfusion should be closely monitored, which can be done by assessing its effectiveness in stopping bleeding (if there is bleeding) and measuring the increase in platelet count after all transfusions (C et al., Class IV). Ineffective platelet transfusion can be diagnosed only if 2 and more platelet transfusions are ineffective. It may be caused by immune or non-immune platelet destruction. In patients with ineffective platelet transfusion, it is important to identify whether it is caused by HLA antibodies, because providing HLA-matched platelets may improve the outcome (grade B, III). Therefore, it is also important to identify other causes of ineffective platelet transfusion after HPA matching, and increasing the transfusion dose or stopping the transfusion may be an appropriate strategy to improve the outcome (Class C, Level IV).